1. Field of the Invention
The present invention relates to an apparatus and a method for separating luminance and color signals from a quadrature modulated video signal in which horizontal, vertical and diagonal variations of the video signal are discriminated and the video signal is line comb filtered, band pass filtered or B2H-filtered in accordance with the discriminated result.
2. Description of the Prior Art
Generally, in a quadrature-modulated color television (TV) system such as, for example, an NTSC system or a PAL system, a color signal C is interleaved in a luminance signal Y in order to efficiently use a limited frequency band width of a video signal.
In such a quadrature-modulated color TV system, a cross luminance phenomenon such as a dot crawling phenomenon and a cross color phenomenon such as a rainbow pattern color spread phenomenon may take place when the luminance and color signals Y and C are not perfectly separated from the video signal.
In order to prevent a degradation in a picture quality due to the cross luminance phenomenon and the cross color phenomenon, a conventional luminance/color signal separation apparatus comprises a line comb filter and/or a band pass filter (or a band rejection filter) using a manner in which, when color signals I and Q are sampled every line at a frequency (4 fsc) of four times that of a color subcarrier, the sampled color signals I and Q are 180.degree.-inverted in phase every two samples.
Namely, as shown in FIG. 1 which is a view illustrating a two-dimensional array of the video signal in a general NTSC system, the luminance and color signals Y and C are inverted in phase every line (. . . , Ln-1, Ln, Ln+1, . . .) and every two samples in the same line. FIGS. 2 and 3 are block diagrams of conventional luminance/color signal separation apparatus. The conventional luminance/color signal separation apparatus of FIG. 2 comprises a band pass filter or a 2H-line comb filter to separate the luminance and color signals from the video signal using the manner of FIG. 1. The conventional luminance/color signal separation apparatus of FIG. 3 comprises a two-dimensional filter (line comb filter+band pass filter) B2H to detect the color signal from the video signal and subtract the detected color signal from the video signal delay-matched, so as to detect the luminance signal with an increased resolution.
Referring to FIG. 2, the conventional luminance/color signal separation apparatus comprises delays 1 and 2 for delaying sequentially an input video signal VIDEO IN, amplifiers 3 and 4 for amplifying the input video signal VIDEO IN and an output signal from the delay 2, respectively, an adder 5 for adding output signals from the delay 1 and the amplifiers 3 and 4, an amplifier 6 for amplifying an output signal from the adder 5 to output the color signal C, a delay matching unit 7 for delaying the output signal from the delay 1 to match its timing with that of the color signal C from the amplifier 6, and a subtracter 8 for subtracting the color signal C from the amplifier 6 from an output signal from the delay matching unit 7 to output the luminance signal Y.
Here, the luminance/color signals are separated from the video signal by the 2H-line comb filtering when a delay period of the delays 1 and 2 is a 1H-line scanning interval, verses by the band pass filtering when the delay period of the delays 1 and 2 is two samples.
The operation of the conventional luminance/color signal separation apparatus with the above-mentioned construction will hereinafter be described with reference to FIG. 1.
In the case where the input video signal VIDEO IN is sampled at the frequency of 4 fsc and processed by the 2H-line comb filter, the delay 1 outputs a sample e by delaying a sample b of the input video signal VIDEO IN by one line and the delay 2 outputs a sample h by delaying the sample e from the delay 1 by one line. The amplifiers 3 and 4 amplify the sample b of the input video signal VIDEO IN and the sample h from the delay by 2 and -1/2, respectively. The adder 5 adds the output signals from the amplifiers 3 and 4 and the sample e from the delay 1. The amplifier 6 amplifies the output signal from the adder 5 by -1/2.
As a result, the separation of the color signal C is performed by signal-processing the samples b, e and h of the video signal on the basis of an equation of 1/2.times.e -1/4.times.(b+h). Then, the delay matching unit 7 matches the timing of the sample e from the delay 1 with that of the color signal C from the amplifier 6. The subtracter 8 subtracts the color signal C from the amplifier 6 from the output signal from the delay matching unit 7, resulting in the separation of the luminance signal Y.
However, in the above-mentioned case where the luminance and color signals are separated from the video signal by the line comb filter, a cross luminance phenomenon such as a dot hanging phenomenon and a cross color phenomenon such as a rainbow pattern color spread phenomenon may take place when the video signal has a vertical or diagonal variation. Also in this case, the luminance signal is reduced in resolution.
On the other hand, in the case where the input video signal VIDEO IN is sampled at the frequency of 4 fsc and processed by the band pass filter, the delay 1 outputs the sample e by delaying a sample d of the input video signal VIDEO IN by two samples and the delay 2 outputs a sample f by delaying the sample e from the delay 1 by two samples. The amplifiers 3 and 4 amplify the sample d of the input video signal VIDEO IN and the sample f from the delay 2 by -1/2, respectively. The adder 5 adds the output signals from the amplifiers 3 and 4 and the sample e from the delay 1. The amplifier 6 amplifies the output signal from the adder 5 by -1/2.
As a result, the separation of the color signal C is performed by signal-processing the samples d, e and f of the video signal on the basis of an equation of 1/2.times.e-1/4.times.(d+f). Then, the delay matching unit 7 matches the timing of the sample e from the delay 1 with that of the color signal C from the amplifier 6. The subtracter 8 subtracts the color signal C from the amplifier 6 from the output signal from the delay matching unit 7, resulting in the separation of the luminance signal Y.
However, in the above-mentioned case where the luminance and color signals are separated from the video signal by the band pass filter, a cross luminance phenomenon such as a dot crawling phenomenon and the cross color phenomenon such as the rainbow pattern color spread phenomenon may take place when the video signal has a horizontal or diagonal variation. Also in this case, the luminance signal is reduced in resolution.
Referring to FIG. 3, the conventional luminance/color signal separation apparatus comprises a B2H circuit for separating the color signal C from the input video signal VIDEO IN. The B2H circuit is provided with a line comb filter 9 and a band pass filter 10 connected in series to the line comb filter 9. A subtracter 12 subtracts the separated color signal C from the input video signal delay-matched by a delay matching unit 11, resulting in the separation of the luminance signal Y.
However, in the above-mentioned conventional luminance/color signal separation apparatus employing the B2H circuit it is desirable to increase the resolution of the luminance signal and reduce the cross color phenomenon as compared with the conventional luminance/color signal separation apparatus of FIG. 2, but thus has a disadvantage in that the cross luminance phenomenon such as the dot crawling phenomenon and the dot hanging phenomenon is significantly increased when the video signal has the horizontal or vertical variation.